1. Field of the Invention
This invention relates to a manufacturing method of a gas discharge display device having an electrode group and a dielectric layer covering same, which is used for generating a discharge in a plasma display panel (PDP) and a plasma addressed liquid crystal (PALC), etc.
PDPs have become popular as a large display device of television picture and computer output upon the achievement of the colored PDP.
2. Description of the Related Arts
As colored displays there have been commercially in production AC type PDPs of a three-electrode surface discharge structure, which are provided with a pair of main electrodes, i.e., a first electrode and a second electrode, for sustaining lighting for the display of each line, and an address electrode, i.e., a third electrode, for each row. In the displaying operation, the AC type PDPs utilize a memory function of the dielectric layer which covers the main electrodes. That is, an addressing is performed in a line scan mode so as to form a charged state in accordance with the contents to be displayed; next, a light sustain voltage Vs having alternating voltage polarities is applied concurrently to all the main electrode pairs. Then, surface discharges are generated along the substrate surface only in the cells having wall charges therein owing to an effective voltage, i.e., a cell voltage, exceeding the discharge firing voltage Vf. Short intervals of the sustain voltages provide a visually continuous lighting state.
In the surface discharge type PDPs, long life can be expected by reducing the deterioration of the fluorescent material layer for the color display caused from ion bombardment during the discharge, by placing the fluorescent material layer on a back substrate opposite from the front substrate carrying the main electrode pairs. The fluorescent material layer coated on the back substrate is called a reflection type, while the fluorescent material layer coated on the front substrate is called a transparent type. The luminous efficiency is advantageous in the reflection type where the front surface of the fluorescent material layer emits the light.
The dielectric layers are used not only for a simple insulating layer in an LCD device, but also for storing electric charges for the AC drive as described above, and have been fabricated by a thick film method where a low-melting temperature glass paste is printed flat and is sintered. The dielectric constant and the thickness of the dielectric layer determined the firing voltage and the discharging current such that a thicker and lower dielectric constant provides less capacitance allowing less (i.e., a reduced) discharging current. Accordingly, the dielectric layer is required to be thicker than a predetermined thickness. However, too thick a dielectric layer requires too high a firing voltage.
There has also been a problem in that the dielectric layer of the prior art thick film method generates bubbles during the firing process resulting in a difficulty in fabricating a uniform film entirely over the screen. The generated bubbles deteriorate the withstanding voltage between the main electrode and the address electrode. Moreover, in the reflection type PDP where the dielectric layer is located on the front substrate, the transparency is deteriorated by the bubbles resulting in less (i.e., reduced) brightness through the front substrate.
Moreover, there are problems in that the high dielectric constant of the low melting point glass requires more electric power in charging the electrostatic capacitance between the electrodes; and causes thermal stress during the firing process as well. Reduced thickness of the dielectric layer may decrease the electrostatic capacitance between the electrodes; however, in coating the glass paste film the thinner layer is apt to cause undulation resulting in an increase in variation of the discharge characteristic, and may increase a fear of exposing the electrode.
Furthermore, the upper surface of dielectric layer 17p formed by a screen printing method or a spin coating method is almost flat regardless of rises and falls of the upper surface of the electrodes 41p and 42p on the substrate 11p as shown in FIG. 8 schematically illustrating a cross-sectional cut view of main portion of a prior art PDP. Accordingly, in the reflection type the thickness of the dielectric layer on the metal film 42p is thinner than that of the dielectric layer on the transparent electrode 41p, whereby a strong discharge is generated above the metal film 42p even though distant from the surface discharge gap. This discharge consumes the power with little contribution to the display light because the light of the discharge is shielded by metal film 42p. 
In order to solve those problems some thin film methods have attempted to form the dielectric layer. However, evaporation methods and a CVD (chemical vapor deposition) method at normal pressure have failed to form the film of adequate thickness without cracks.
It is a general object of the invention to provide a method to form a homogenous dielectric layer having a small dielectric constant, and an adequate thickness, leaving a proper thermal stress on the glass substrate, so as to be used in a gas discharge display device.
After main electrodes for generating a surface discharge therebetween are fabricated on a substrate, a dielectric layer is deposited on the substrate as well as on the electrodes by a plasma chemical deposition method. The material of the dielectric layer is typically silicon dioxide. Thickness of the dielectric layer is 5 to 30 xcexcm thick.
The above-mentioned features and advantages of the present invention, together with other objects and advantages which will become apparent, will be more fully described hereinafter, with references being made to the accompanying drawings which form a part hereof, wherein like numerals refer to like parts throughout.